Low reflectance removable lens stack

ABSTRACT

A removable lens stack includes a base layer, a first removable lens layer, and a second removable lens layer. The base layer may include a substrate and a moth eye coating. The first removable lens layer may include a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and a fluoropolymer coating on a second side of the substrate. The first removable lens layer may be stacked on top of the base layer with the fluoropolymer coating being molded to fit the moth eye coating. The second and any subsequent removable lens layer may include a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate. The second removable lens layer may be stacked on top of the first removable lens layer and so on.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 17/655,328, filed Mar. 17, 2022, which is a continuation of U.S. patent application Ser. No. 17/386,304, filed Jul. 27, 2021, now U.S. Pat. No. 11,307,329, issued Apr. 19, 2022, the contents of each of which are expressly incorporated herein by reference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

In various environments where one uses protective eyewear such as goggles, visors, and face shields, it is important to maintain visibility as debris accumulates on the eyewear. For example, participants in off-road sports like motocross racing need to maintain visibility of the course as mud, bugs, and other debris accumulate on their goggles or helmet visor. Similarly, in an operating room environment, splatter can impair the view of surgeons or other operating personnel during a procedure. In response to these needs, tearoff films are commonly employed, either individually or in laminated stacks, which are applied to the goggle lens, visor, or face shield. As debris accumulates on the outermost tearoff film or the outermost tearoff film becomes damaged, the wearer simply tears it off to reveal the next pristine film underneath.

In order to ensure visual acuity through such stacked lenses, it is desirable to minimize internal reflection. One promising technology for reducing reflection is so-called moth-eye (ME) coatings, which simulate the anti-reflective properties of a moth's eye by providing a pattern of microscopic bumps that effectively eliminate the index of refraction interface between the lens and the air. Unfortunately, in the case of a stack of lenses, the adhesives used between the layers have a tendency to fill in around the bumps of the ME coating, drastically increasing the peel strength of each layer (making it 650 to 1,070 grams/inch, for example) and thus making the stack unusable as the layers cannot easily be torn off and the force to remove a layer may be greater than the tensile strength of the lens material.

BRIEF SUMMARY

The present disclosure contemplates various devices and methods for overcoming the drawbacks accompanying the related art. One aspect of the embodiments of the present disclosure is a removable lens stack. The removable lens stack may comprise a base layer including a substrate having a first side and a second side opposite the first side, the base layer further including a moth eye coating on the first side of the substrate. The removable lens stack may further comprise one or more removable lens layers, each removable lens layer including a substrate having a first side and a second side opposite the first side, a moth eye coating on the first side of the substrate, and a fluoropolymer coating on the second side of the substrate. The one or more removable lens layers may be stacked on top of the base layer such that the second side of the substrate of each removable lens layer faces the first side of the substrate of an immediately preceding layer from among the base layer and the one or more removable lens layers. Each of the fluoropolymer coatings may be molded to fit the moth eye coating of the immediately preceding layer.

In each of the one or more removable lens layers and the base layer, the moth eye coating may comprise a polymer.

In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of bumps with half-wave pitch.

In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of bumps with half-wave height.

In each of the one or more removable lens layers and the base layer, the moth eye coating may define a pattern of cones.

The base layer may further include a moth eye coating on the second side of the substrate.

In each of the one or more removable lens layers and the base layer, the substrate may comprise polyethylene terephthalate (PET).

The removable lens stack may comprise, in each of the one or more removable lens layers and the base layer, an adhesion treatment between the substrate and the moth eye coating. The adhesion treatment may comprise a pressure sensitive adhesive.

The removable lens stack may comprise, in each of the one or more removable lens layers, an adhesion treatment between the substrate and the fluoropolymer coating. The adhesion treatment may comprise a pressure sensitive adhesive.

A peel strength of each of the one or more removable lens layers may be less than 100 grams per inch. A peel strength of each of the one or more removable lens layers may be between 15 and 50 grams per inch and may, more particularly, be between 15 and 30 grams per inch.

A visible light transmission (VLT) of the removable lens stack may be greater than 95% and may, more particularly, be greater than 98%.

Another aspect of the embodiments of the present disclosure is a method of manufacturing a removable lens stack. The method may comprise providing a base layer including a substrate having a first side and a second side opposite the first side, the base layer further including a moth eye coating on the first side of the substrate. The method may further comprise stacking one or more removable lens layers on top of the base layer, each removable lens layer including a substrate having a first side and a second side opposite the first side, a moth eye coating on the first side of the substrate, and a fluoropolymer coating on the second side of the substrate. The one or more removable lens layers may be stacked on top of the base layer such that the second side of the substrate of each removable lens layer faces the first side of the substrate of an immediately preceding layer from among the base layer and the one or more removable lens layers. The method may further comprise laminating the stacked one or more removable lens layers to the base layer, each of the fluoropolymer coatings being molded to fit the moth eye coating of the immediately preceding layer.

The laminating may comprise laminating the stacked one or more removable lens layers to the base layer under pressure at a temperature less than 40° C.

The method may comprise, in each of the one or more removable lens layers, applying a corona treatment between the substrate and the moth eye coating.

The method may comprise, in each of the one or more removable lens layers, applying a corona treatment between the substrate and the fluoropolymer coating.

Another aspect of the embodiments of the present disclosure is a removable lens stack comprising a base layer, a first removable lens layer, and a second removable lens layer. The base layer may include a substrate and a moth eye coating on a first side of the substrate. The first removable lens layer may include a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and a fluoropolymer coating on a second side of the substrate opposite the first side. The first removable lens layer may be stacked on top of the base layer such that the second side of the substrate of the first removable lens layer faces the first side of the substrate of the base layer, the fluoropolymer coating being molded to fit the moth eye coating. The second removable lens layer may include a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side. The second removable lens layer may be stacked on top of the first removable lens layer such that the second side of the substrate of the second removable lens layer faces the first side of the substrate of the first removable lens layer.

The moth eye coating may comprise a polymer. The moth eye coating may define a pattern of bumps with half-wave pitch. The moth eye coating may define a pattern of bumps with half-wave height. The moth eye coating may define a pattern of cones.

The base layer may include a moth eye coating on a second side of the substrate opposite the first side.

In each of the base layer, the first removable lens layer, and the second removable lens layer, the substrate may comprise polyethylene terephthalate (PET).

The removable lens stack may further comprise a third removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side. The third removable lens layer may be stacked on top of the second removable lens layer such that the second side of the substrate of the third removable lens layer faces the first side of the substrate of the second removable lens layer. The removable lens stack may further comprise a fourth removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side. The fourth layer may be stacked on top of the third removable lens layer such that the second side of the substrate of the fourth removable lens layer faces the first side of the substrate of the third removable lens layer.

A peel strength of the first removable lens layer may be less than 100 grams per inch. The peel strength of the first removable lens layer may be between 15 and 50 grams per inch. The peel strength of the first removable lens layer may be between 15 and 30 grams per inch.

A visible light transmission (VLT) of the removable lens stack may be greater than 95%. The VLT of the removable lens stack may be greater than 98%.

Another aspect of the present disclosure is a method of manufacturing a removable lens stack. The method may comprise providing a base layer including a substrate and a moth eye coating on a first side of the substrate and stacking a first removable lens layer on top of the base layer, the first removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and a fluoropolymer coating on a second side of the substrate opposite the first side. The first removable lens layer may be stacked on top of the base layer such that the second side of the substrate of the first removable lens layer faces the first side of the substrate of the base layer. The method may further comprise laminating the stacked first removable lens layer to the base layer, the fluoropolymer coating being molded to fit the moth eye coating. The method may further comprise stacking a second removable lens layer on top of the first removable lens layer, the second removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the second removable lens layer being stacked on top of the first removable lens layer such that the second side of the substrate of the second removable lens layer faces the first side of the substrate of the first removable lens layer.

The laminating may comprise laminating the stacked first removable lens layer to the base layer under pressure at a temperature less than 40° C. The laminating may be performed prior to the stacking of the second removable lens layer on top of the first removable lens layer.

The method may further comprise applying a corona treatment between the substrate and the moth eye coating of the base layer and/or between the substrate and the fluoropolymer coating of the first removable lens layer.

The method may further comprise stacking a third removable lens layer on top of the second removable lens layer, the third removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side. The third removable lens layer may be stacked on top of the second removable lens layer such that the second side of the substrate of the third removable lens layer faces the first side of the substrate of the second removable lens layer. The method may further comprise stacking a fourth removable lens layer on top of the third removable lens layer, the fourth removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side. The fourth removable lens layer may be stacked on top of the third removable lens layer such that the second side of the substrate of the fourth removable lens layer faces the first side of the substrate of the third removable lens layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

FIG. 1 is a cross-sectional view of a base layer and two removable lens layers of a removable lens stack according to an embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the removable lens stack having the layers of FIG. 1 ;

FIG. 3 is a cross-sectional view of a base layer and removable lens layers of a removable lens stack according to another embodiment of the present disclosure; and

FIG. 4 is a cross-sectional view of the removable lens stack having the layers of FIG. 3 .

DETAILED DESCRIPTION

The present disclosure encompasses various embodiments of removable lens stacks and manufacturing methods thereof. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

FIG. 1 is a cross-sectional view of a base layer 100 and two removable lens layers 200, which may be stacked together to form a removable lens stack 10 as shown in cross-section in FIG. 2 . The base layer 100 of the removable lens stack 10 may be affixed to a surface such as a goggle lens or visor or a transparent window of a surgical helmet, hood, or gown, for example, or alternatively may be attached at a perimeter thereof to a frame such that the removable lens stack 10 itself serves as the lens, visor, face shield, etc. (i.e. without being affixed to a surface). In the example of FIGS. 1 and 2 , two removable lens layers 200 are shown, which are stacked on the base layer 100 to form the removable lens stack 10. However, it is contemplated that there may be more than two removable lens layers 200 or that there may be only a single removable lens layer 200. As shown, each of the removable lens layers 200 may comprise a substrate 210 and a moth eye coating 220 on a first side 212 thereof. The base layer 100 may likewise comprise a substrate 110 and a moth eye coating 120 a on a first side 112 thereof, as well as an optional moth eye coating 120 b on a second side 114 opposite the first side 112. Owing to the moth eye coatings 120 a, 120 b, 220, the removable lens stack 10 may have very low reflectance and, accordingly, may exhibit a visible light transmission (VLT) of greater than 95% or in some cases greater than 98% (e.g. >99% with reflections sub 1%).

Unlike conventional removable lenses, each removable lens layer 200 may additionally comprise a fluoropolymer coating 230 on a second side 214 of the substrate 210 opposite the first side 212. As such, when the removable lens layer(s) 200 are stacked on top of the base layer 100 with the second side 214 of each substrate 210 facing the first side 112, 212 of the immediately preceding substrate 110, 210 (which may be the substrate 210 of an immediately preceding removable lens layer 200 or the substrate 110 of the base layer 100 as the case may be), the fluoropolymer coating(s) 230 may abut the moth eye coatings 120 a, 220. Upon laminating the stacked removable lens layer(s) 200 to the base layer 100, each fluoropolymer coating 230 may thus be molded to fit the moth eye coating 120 a, 220 of the immediately preceding layer 100, 200. The resulting mechanical interlocking of the moth eye coatings 120 a, 220 with the molded female patterns corresponding thereto formed in the adjacent fluoropolymer coatings 230 may function similarly to a zipper to fix the adjacent layers together. Owing to this mechanical interlocking, the use of an acrylic or other tacky adhesive on the moth eye coating 120 a, 220 may be entirely avoided, preventing the increased peel strength associated with such conventional adhesives collecting around the bumps of the moth eye coating 120 a, 220. Thus, the removable lens layer(s) 200 may advantageously have a much lower peel strength, which may be less than 100 grams per inch and may, for example, be between 15 and 50 grams per inch or more particularly between 15 and 30 grams per inch (e.g. 25 grams per inch), making it possible for the wearer to remove each layer 200 as desired with a reasonable amount of pulling force. (It is noted that the use of a tacky adhesive to affix the base layer 100 to a surface may not present a problem since the base layer 100 need not be removable and thus an increased peel strength caused by buildup of adhesive around the bumps of the optional moth eye coating 120 b may be acceptable.)

The substrate 110, 210 of each layer 100, 200 may comprise a transparent polymer such as polyethylene terephthalate (PET) and may be 1 to 10 mil thick, for example, around 2 mil thick for the substrate 210 of each removable lens layer 200 with the substrate 110 of the base layer 100 being the same thickness or typically thicker (e.g. 7 mil). The moth eye coating 220 of each of the removable lens layers 200, as well as the moth eye coating(s) 120 a, 120 b of the base layer 100, may comprise a polymer and may typically be made of a hard polymer such as glassy carbon having a Mohs hardness of 7, for example. The moth eye coating 120 a, 120 b, 220 may define a pattern of nano sized micro-projections or bumps (e.g. transparent cones) on the surface of the substrate 110, 210 with dimensions on the order of the wavelength of light (e.g. visible light), such as half-wave pitch and/or half-wave height, to produce the antireflective effect. For example, the pitch and/or height of the bumps may be 200-375 nm. Various shapes are possible for the bumps of the moth eye coating 120 a, 120 b, 220, including rounded or rectangular raised surfaces instead of cones, for example.

The moth eye coating 120 a, 120 b, 220 may be refractive index matched (e.g. to within 0.2) with the substrates 110, 210 and with the fluoropolymer coating(s) 230, as well as with any adhesives that may be used (as described below), such that the entire removable lens stack 10 may have a consistent index of refraction (e.g. within 0.2). However, because the refractive index interface between the air and the removable lens stack 10 may be effectively eliminated by the outermost moth eye coating 220 (as the interface appears like a gradient rather than a sudden change in material from the perspective of incident light), it is not necessary to index match the removable lens stack 10 to air (n=1). Therefore, it is contemplated that a wide variety of materials may be used for the substrates 110, 210 and other components of the removable lens stack 10.

In general, when building a conventional removable lens stack, a removable bonding material is used to wet each pair of adjacent surfaces together. The term “wetting,” in this context, may refer to when two surfaces come in such close contact with each other that the contact displaces all of the air in between the two surfaces, allowing for good bonding. Whereas simply laying one lens on top of another lens does not disperse the air trapped between the lenses, an acrylic removable adhesive may be used to wet the surfaces together and promote bonding. By matching the refractive index of the adhesive with the refractive index(es) of the lenses (e.g. to within 0.2), visible light may stay at a constant speed at the interfaces, minimizing reflections. An example of such a system may be found in U.S. Pat. No. 9,295,297, entitled “Adhesive Mountable Stack of Removable Layers,” the entire contents of which is expressly incorporated by reference herein. However, because adhesive is tacky to the touch, issues arise when bonding two surfaces together where one or both surfaces have a moth eye coating. In particular, as described above, the adhesive fills in around the micro-projections of the moth eye coating, drastically increasing the peel strength beyond what is functionally suitable for a removable lens stack.

Therefore, in order to wet the surfaces of the substrates 110, 210 together and achieve the preferred peel strength in the disclosed removable lens stack 10, the fluoropolymer coating(s) 230 may be provided on the second side 214 of each substrate 210. The fluoropolymer coating 230 may be an index-matched (e.g. to within 0.2) soft fluoropolymer such as fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy alkane (PFA), or tetrafluoroethylene perfluoro(methyl vinyl ether) (MFA) that is not tacky to the touch but is moldable under laminating pressure to produce a debossed (female) pattern corresponding to the bumps of the abutting moth eye coating 120 a, 220.

In some cases, an adhesion treatment 140 a, 240 may be provided between the substrate 110 and moth eye coating 120 a of the base layer 100 and/or between the substrate 210 and moth eye coating 220 of each removable lens layer 200. Likewise, if the substrate 110 of the base layer 100 further includes a moth eye coating 120 b on the second side 114 thereof, an adhesion treatment 140 b may be provided between the substrate 110 and the moth eye coating 120 b. In each removable lens layer 200, an adhesion treatment 250 may similarly be provided between the substrate 210 and the fluoropolymer coating 230. The adhesion treatments 140 a, 140 b, 240, 250 may comprise a pressure sensitive adhesive such as a silicone adhesive (e.g. a polydimethyl/methylvinyl siloxane polymer and resin dispersed in toluene/isopropyl alcohol such as an adhesive sold under the name DOWSIL™ 7655 Adhesive or DOWSIL™ 7656 Adhesive by the Dow Chemical Company). The adhesive may be index matched (e.g. to within 0.2) with the substrates 110, 210 and other elements of the removable lens stack 10 as noted above.

The base layer 100 and one or more removable lens layers 200 may be manufactured by coating each substrate 110, 210 with the moth eye coating(s) 120 a, 120 b, 220 and fluoropolymer coating 230, which may in some cases be adhered to the substrates 110, 210 by adhesion treatments 140 a, 140 b, 240, 250 as described above. In order to improve adhesion, it is also contemplated that a corona treatment may be applied between the substrate 110, 210 and the moth eye coating 120 a, 120 b, 220, and/or between the substrate 210 and the fluoropolymer coating 220. This may ensure that the fluoropolymer coating 220 remains with the outermost removable lens layer 200 as it is pulled off the removable lens stack 10, for example. The corona treatment may be applied instead of or in addition to the above-described adhesion treatments 140 a, 140 b, 240, 250. The removable lens layer(s) 200 may then be stacked on top of the base layer 100 such that the second side 214 of the substrate 210 of each removable lens layer 200 faces the first side 112, 212 of the substrate 110, 210 of an immediately preceding layer from among the base layer 100 and the one or more removable lens layers 200 (as the case may be). In the illustrated example shown in FIGS. 1 and 2 , a first removable lens layer 200 (shown in the center of each figure) is stacked on the base layer 100 and a second removable lens layer 200 (shown in the left-hand side of each figure) is stacked on the first removable lens layer 200. Additional removable lens layers 200 may similarly be provided and added to the stack.

The removable lens layer(s) 200 may then be laminated to the base layer 100 under pressure with or without heat, for example, under pressure at a temperature less than 40° C. It should be noted that the base layer 100 and removable lens layer(s) 200 may be laminated together in a single lamination process or in multiple lamination processes, for example, with each removable lens layer 200 added to the stack in a separate lamination process (or with multiple removable lens layers 200 being laminated together before being laminated to the base layer 100). As a result of the lamination, each fluoropolymer coating 230 may be molded to fit the moth eye coating 120 a, 220 of the immediately preceding layer. In particular, the hard bumps of the moth eye coating 120 a, 220 may press into the soft fluoropolymer coating 230 to produce the corresponding debossed (female) pattern in the fluoropolymer coating 230. In this way, the above-described mechanical interlocking between the layers 100, 200 may be achieved to produce the desired peel strength (e.g. 25 grams per inch) without the use of tacky adhesives between the layers 100, 200 that might otherwise fill in between the bumps and increase the peel strength too much. At the same time, the air between the layers 100, 200 may be expelled during the laminating process, allowing for wetting of the opposing layers 100, 200 (and slight adhesion as a result), while the refractive index interface may be effectively eliminated due to the index gradient created by the architecture of the moth eye coatings 120 a, 220. The resulting visible light transmission (VLT) of the removable lens stack 10 may be greater than 95% (e.g. 96% with 4% reflection), as opposed to 92% with 8% reflection that might be found in an uncoated lens. In some cases, the VLT may be greater than 98% (e.g. >99%), especially when the moth eye coating 120 b is provided so that there are moth eye coatings 120 a, 120 b, 220 on both sides of the stack 10.

When the removable lens stack 10 is incorporated into eyewear and being worn, the wearer may easily peel off the outermost removable lens layer 200 to reveal an unblemished removable lens layer 200 (or the base layer 100) underneath. In the case of a removable lens stack 10 having multiple removable lens layers 200, the pulling force used to remove the outermost removable lens layer 200 may generally involve an initial outward force (perpendicular to the stack 10) as the wearer lifts the outermost removable lens layer 200 off the stack 10 on one side to separate it from the other removable lens layers 200 (e.g. by grasping an easily accessible tab on one side of the stack 10), followed by a continuous sideways force (with a component parallel to the stack 10) as the wearer peels the outermost removable lens layer 200 off. It is contemplated that the continuous sideways force that is responsible for the majority of the separation of the removable lens layers 200 may have more of a tendency to lift off the outermost removable lens layer 200 than to separate subsequent layers 200 underneath. Therefore, the wearer can readily peel off one layer 200 at a time without accidentally tearing off additional layers 200 of the removable lens stack 10.

Hybrid stacks are also contemplated, in which one or more layers having moth eye coatings may be combined with one or more layers having alternative types of antireflective coatings such as single or multi-layer interference antireflective coatings. By way of example, FIG. 3 is a cross-sectional view of the same base layer 100 as in FIG. 1 but this time with a removable lens layer 300 and two removable lens layers 400, which may be stacked together to form a removable lens stack 20 as shown in cross-section in FIG. 4 . The base layer 100 of the removable lens stack 20 may be the same as that of the removable lens stack 10 as shown in FIGS. 1 and 2 and may similarly be affixed to a surface such as a goggle lens or visor or a transparent window of a surgical helmet, hood, or gown, for example, or alternatively may be attached at a perimeter thereof to a frame such that the removable lens stack 20 itself serves as the lens, visor, face shield, etc. Advantageously, the removable lens stack 20 employs moth eye coating in some but not all layers, reducing the difficulty and expense associated with producing moth eye coating. In the illustrated embodiment, for example, the base layer 100 is the only layer to have moth eye coating, with removable lens layers 300, 400 instead having single or multi-layer interference antireflective coatings 340, 440 that may be less expensive to produce (e.g., by spin coating, dip coating, or vacuum deposition). In particular, a first removable lens layer 300 may include a substrate 310, a single or multi-layer interference antireflective coating 340 on a first side 312 of the substrate 310, and a fluoropolymer coating 330 on a second side 314 of the substrate 310 opposite the first side 312 (with optional adhesion treatment 350). With the first removable lens layer 300 stacked on top of the base layer 100 and the second side 314 of the substrate 310 facing the first side 112 of the substrate 110 of the base layer 100, the fluoropolymer coating 330 may be molded to fit the moth eye coating 120 a as described above.

One or more additional removable lens layers 400 may also be added to the stack, each including a substrate 410, a single or multi-layer interference antireflective coating 440 on a first side 412, and an adhesive 450 such as an acrylic or polyurethane adhesive on a second side 414. One such removable lens layer 400 may be stacked on the removable lens layer 300 such that the second side 414 of the substrate 410 faces the first side 312 of the substrate 300. Further removable lens layers 400 may be stacked thereon, with the second side 414 of each substrate 410 facing the first side 412 of each preceding substrate 400. By using an antireflective coating 340, 440 that does not have bumps like the moth eye coating 120 a, any concern about the adhesive 450 filling in around the bumps and undesirably increasing the peel strength can be avoided. As a result, various kinds of adhesive 450 may be used including an acrylic or polyurethane adhesive such as a pressure sensitive adhesive (PSA), which may adhere (e.g., with the application of pressure) to the antireflective coating 340, 440 of the preceding layer 300, 400. The hybrid removable lens stack 20 may effectively achieve the superior antireflective properties of moth eye by incorporating it in one or more layers while at the same time benefiting from one or more layers having less expensive antireflective coatings 340, 440 and/or adhesives 450. The hybrid removable lens stack 20 may thus represent a “best of both worlds” compromise that balances the need for a high degree of antireflection with the manufacturing costs.

In the example of FIGS. 3 and 4 , one removable lens layer 300 (having a non-ME AR coating 340 and a fluoropolymer coating 330 to interface with the moth eye coating 120 a of the base layer 100) and two removable lens layers 400 (having a non-ME AR coating 440 and an acrylic or polyurethane adhesive 450) are shown, which are stacked on the base layer 100 to form the removable lens stack 20. However, hybrid stacks of various other combinations of layers are also contemplated. For example, more or fewer removable lens layers 400 may be used. Also, one or more removable lens layers 200 (see FIGS. 1 and 2 ) may be added between the base layer 100 and the removable lens layer 300, In this case, the fluoropolymer coating 330 of the removable lens layer 300 may interface with the moth eye coating 220 of the outermost removable lens layer 200 instead of directly with the moth eye coating 120 a of the base layer 100. Alternatively, substrates with moth eye coating(s) may be incorporated farther outward in the stack with one or more substrates having non-ME AR coating(s) underneath. To this end a modified layer 400 may be used having a moth eye coating in place of the non-ME AR coating 440 (but with the acrylic or polyurethane adhesive 450 still being used to interface with a non-ME AR coating underneath). Hybrid removable lens stacks 20 of various configurations may be economically designed and produced in accordance with the particular needs of the manufacturer and consumer, both in terms of the degree of antireflection required and the desired unit cost.

It should also be noted that the use of moth eye coatings on both sides of a single layer (i.e., forward and rear facing moth-eye patterns) is not necessarily limited to the base layer 100. Either of the removable lens stacks 10, 20 may include such double-sided moth-eye layers at any position in the stack. For example, the stack may consist of multiple layers 100 stacked on top of each other (which may in some cases be the only type of layer in the stack such as a stack consisting of three layers 100). Between each pair of adjacent layers 100, a fluoropolymer coating may be applied that may mold to the shape of the moth-eye coating as described above, except that in this case the fluoropolymer coating may mold to the shapes of two moth-eye coatings that face each other with the fluoropolymer coating therebetween. As one example method of stacking multiple such double-sided moth-eye layers 100, the fluoropolymer coating may be coated on the forward-facing moth-eye coating 120 a of a first layer 100, causing one side of the fluoropolymer coating to mold to the shape of the forward-facing moth-eye coating 120 a, and then a second layer 100 may be stacked on the fluoropolymer coating and laminated, causing the other side of the fluoropolymer coating to mold to the shape of the rear-facing moth-eye coating 120 b of the second layer 100. Stacking of further layers 100 can continue in the same way (or in combination with other types of layers as described above), with the fluoropolymer coating being molded to the shapes of two adjacent moth-eye coatings wherever necessary. Preferably, a release treatment may be applied to each forward-facing moth-eye coating 120 a, and/or an adhesion promoting treatment may be applied to each rear-facing moth-eye coating 120 b, thus encouraging the fluoropolymer coating to come off with each layer 100 as it is removed from the stack. By using double-sided moth-eye layers in this way, a high degree of antireflection can be achieved. Moreover, depending on the moth-eye fabrication processes used, producing two moth-eye coatings 120 a, 120 b on the same substrate 110 may be more cost effective than producing individual moth-eye coatings on separate substrates, making the use of double-sided moth-eye layers potentially more efficient. Manufacturing processes may also be simplified (and costs reduced) by the use of the same repeated layer 100 in place of multiple different layers.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments. 

What is claimed is:
 1. A removable lens stack comprising: a base layer including a substrate and a moth eye coating on a first side of the substrate; a first removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and a fluoropolymer coating on a second side of the substrate opposite the first side, the first removable lens layer being stacked on top of the base layer such that the second side of the substrate of the first removable lens layer faces the first side of the substrate of the base layer, the fluoropolymer coating being molded to fit the moth eye coating; and a second removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the second removable lens layer being stacked on top of the first removable lens layer such that the second side of the substrate of the second removable lens layer faces the first side of the substrate of the first removable lens layer.
 2. The removable lens stack of claim 1, wherein the moth eye coating comprises a polymer.
 3. The removable lens stack of claim 1, wherein the moth eye coating defines a pattern of bumps with half-wave pitch.
 4. The removable lens stack of claim 1, wherein the moth eye coating defines a pattern of bumps with half-wave height.
 5. The removable lens stack of claim 1, wherein the moth eye coating defines a pattern of cones.
 6. The removable lens stack of claim 1, wherein the base layer further includes a moth eye coating on a second side of the substrate opposite the first side.
 7. The removable lens stack of claim 1, wherein, in each of the base layer, the first removable lens layer, and the second removable lens layer, the substrate comprises polyethylene terephthalate (PET).
 8. The removable lens stack of claim 1, further comprising a third removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the third removable lens layer being stacked on top of the second removable lens layer such that the second side of the substrate of the third removable lens layer faces the first side of the substrate of the second removable lens layer.
 9. The removable lens stack of claim 8, further comprising a fourth removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the fourth layer being stacked on top of the third removable lens layer such that the second side of the substrate of the fourth removable lens layer faces the first side of the substrate of the third removable lens layer.
 10. The removable lens stack of claim 1, wherein a peel strength of the first removable lens layer is less than 100 grams per inch.
 11. The removable lens stack of claim 10, wherein the peel strength of the first removable lens layer is between 15 and 50 grams per inch.
 12. The removable lens stack of claim 11, wherein the peel strength of the first removable lens layer is between 15 and 30 grams per inch.
 13. The removable lens stack of claim 1, wherein a visible light transmission (VLT) of the removable lens stack is greater than 95%.
 14. The removable lens stack of claim 13, wherein the VLT of the removable lens stack is greater than 98%.
 15. A method of manufacturing a removable lens stack, the method comprising: providing a base layer including a substrate and a moth eye coating on a first side of the substrate; stacking a first removable lens layer on top of the base layer, the first removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and a fluoropolymer coating on a second side of the substrate opposite the first side, the first removable lens layer being stacked on top of the base layer such that the second side of the substrate of the first removable lens layer faces the first side of the substrate of the base layer; laminating the stacked first removable lens layer to the base layer, the fluoropolymer coating being molded to fit the moth eye coating; and stacking a second removable lens layer on top of the first removable lens layer, the second removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the second removable lens layer being stacked on top of the first removable lens layer such that the second side of the substrate of the second removable lens layer faces the first side of the substrate of the first removable lens layer.
 16. The method of claim 15, wherein said laminating comprises laminating the stacked first removable lens layer to the base layer under pressure at a temperature less than 40° C.
 17. The method of claim 15, wherein said laminating is performed prior to said stacking the second removable lens layer on top of the first removable lens layer.
 18. The method of claim 15, further comprising applying a corona treatment between the substrate and the moth eye coating of the base layer.
 19. The method of claim 15, further comprising applying a corona treatment between the substrate and the fluoropolymer coating of the first removable lens layer.
 20. The method of claim 15, further comprising stacking a third removable lens layer on top of the second removable lens layer, the third removable lens layer including a substrate, a single or multi-layer interference antireflective coating on a first side of the substrate, and an acrylic or polyurethane adhesive on a second side of the substrate opposite the first side, the third removable lens layer being stacked on top of the second removable lens layer such that the second side of the substrate of the third removable lens layer faces the first side of the substrate of the second removable lens layer. 